THE INTERACTION FORCES BETWEEN SILICA AND PLASMA-TREATED POLYPROPYLENE SURFACES IN AQUEOUS-SOLUTIONS

The interaction forces between silica and plasma-treated polypropylene surfaces in aqueous NaCl solutions have been measured using a scannin g force microscope. The measured interaction forces are well described by DLVO theory at large and moderate separation distances. However, a t short range (<5 nm) an additional repulsive force is measured, presu mably due to solvation of the surfaces. This additional force was not present when the interaction forces were measured between untreated po lypropylene and silica under identical conditions, The presence of C-O H groups on the surface of the polypropylene is proposed to account fo r this additional repulsive force, In addition, the surface potential and charges fitted to the data were much higher than in the untreated polypropylene case, As no ionizable groups are present on either polyp ropylene surface, the adsorption of bicarbonate ion from solution is p roposed to account for the surface charge. (C) 1997 Academic Press